One challenge in the field of regenerative medicine is the regeneration of nerve cells. It is hoped, for example, that the regeneration of nerve cells using neuronal stem cells or embryonic stem cells (ES cells) will lead to treatments for central nervous system diseases such as Parkinson disease and Alzheimer disease (Patent Document 1). However, embryonic and other stem cells are difficult to acquire (collect). Moreover, even when such stem cells are implanted directly to the affected area, substantially no differentiation to nerve cells occurs and engraftment is difficult. Even in cases where such cells do take, few if any end up differentiating to glia cells.
Somatic (adult) stem cells such as neuronal stem cells, skin stem cells and adipose stem cells are stem cells that are relatively easy to acquire. Were it possible to differentiate such stem cells to nerve cells, their utility in the healthcare industry would be high. However, a method for inducing the differentiation of nerve cells from these somatic stem cells in a short period of time and at a high efficiency has yet to be established. Hence, there exists a desire for such a method to be established; that is, for the development of a neuronal differentiation inducer suitable for such a purpose. For example, Patent Document 2 discloses a neuronal differentiation inducer containing a pyrrolidone derivative as the active ingredient, but it does not disclose the effects of inducing the differentiation of nerve cells from somatic stem cells.
Recently, the use of peptides having the function of inducing the differentiation of stem cells to nerve cells (neuronal differentiation-inducing peptides) has been attracting attention. For example, Patent Document 3 describes a peptide (VHL peptide) which is capable of inducing neuronal differentiation from neuronal stem cells or skin stem cells.    Patent Document 1: Japanese Patent Application Laid-open No. 2004-357543    Patent Document 2: Japanese Patent Application Laid-open No. H9-323928    Patent Document 3: Japanese Patent Application Laid-open No. 2005-330206    Non-Patent Document 1: Trends in Cell Biology, 8, 410-415 (1998)    Non-Patent Document 2: The Journal of Biological Chemistry, 281(35), 25223-25230 (2006)